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  1. #1
    Join Date
    Apr 2014
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    5

    Default Vapor Barrier and insulation in walls

    I have an old Home that I am rehabbing for a rental in Lower TN. The wall structure consists of Brick, Felt, diagonal 1x6 tongue and groove planks, 2x4's, then Horizontal 1x4's completely covering the interior wall, in that order. The interior 1x4's only had Wall paper, no drywall or any other coverings. There is a living room section that has plaster or stucco on top of what appears to be 16" drywall strips.

    I am looking at blowing in insulation before dry walling over the interior, but I am worried about condensation, or other problems that this may cause. I was wondering if i could blow in insulation, cover the boards with Plastic as a vapor barrier, then cover the plastic with Drywall. Will that prevent the condensation issue, or will that just cause to condensation to form on the 1x4s and compound the issue?

    If I am unable to insulate and prevent problems, I may skip the insulation and just put the plastic up to stop any airflow, but don't know if that would cause the same issue as having the insulation in the wall. What would you do, or what is the best way to go about this, keeping in mind that I do not want to remove the interior lumber.

    Thanks

  2. #2
    Join Date
    Apr 2014
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    4

    Default Re: Vapor Barrier and insulation in walls

    Even in lower TN, insulation is important. Yes, blown in would be a good solution. Yes, a vapor barrier is needed. While blown in in an existing structure may not fill all the voids, it still makes good sense. What are you considering for the attic? So much heat is lost from the attic, you really need to address that, as well.

  3. #3
    Join Date
    Apr 2014
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    5

    Default Re: Vapor Barrier and insulation in walls

    the attic is a 2nd story unfinished space. Part of the renovation is to finish it out and will insulate it at that time. The main question is, normally a vapor barrier goes against the insulation. In this case there will be lumber between the insulation and the vapor barrier. Will this cause the lumber to rot or will it help.

    Thanks

  4. #4
    Join Date
    Aug 2007
    Location
    Portland, Oregon, formerly of Chicago
    Posts
    1,806

    Default Re: Vapor Barrier and insulation in walls

    There is a debate in among the building science people as to whether an absolute vapor barrier, such as heavy plastic, should ever be used in wall construction. This is especially important in areas of the country that are hot and humid in summer and the house is air-conditioned. There is not only vapor drive toward the exterior in winter, but vapor drive toward the interior in summer. That plastic behind the drywall constitutes an absolute vapor barrier and moisture from the outside can get trapped in the wall. In a worst case scenario, moisture laden air can condensate on the cold interior side of the wall cavity.

    This is the reverse of what happens when, in winter, moisture tries to get to the outside and condensates on the back of the wall sheathing. No one would advocate using heavy plastic as a vapor barrier under the siding. Traditionally, the back side of wooden siding would be primed as a vapor retarder.

    A good coat of premium interior paint and primer should suffice as a vapor retarder, rather than an absolute barrier.

  5. #5
    Join Date
    Dec 2007
    Location
    Tennessee
    Posts
    1,769

    Default Re: Vapor Barrier and insulation in walls

    Most people in the building science industry will agree that you need a vapor barrier. You plan to put it over the 1x4's and just under the sheetrock is a sound plan. The condensation will not occur in the 1x4's as they will be too warm. Even in summer, you are not in a region where the dew point will be high enough in summer to cause condensation in your walls from the AC. You only need to protect the walls in winter so you need the vapor barrier.

  6. #6
    Join Date
    Jan 2008
    Posts
    2,194

    Default Re: Vapor Barrier and insulation in walls

    Why not pull the 1X4's and drywall over faced fiberglass rolled insulation? You get an adequate vapor barrier without total sealing, cheaper and more effective insulation, and little added cost for what should be an easy demo. And you have bonfire wood for the finishing party when you're done

    Phil

  7. #7
    Join Date
    Apr 2014
    Posts
    5

    Default Re: Vapor Barrier and insulation in walls

    Thanks for all the replies. So far i am with Keith3267 and it seems that ordjen's comments back it up also, so unless someone sees a problem with the plastic, I will probably will go that route.

    As for putting up the 1x4's, If I did that then I would have to pull all the trim out, dispose of all the material, and god only knows what else that would lead to. Plus, there is nothing like having solid walls, no renters punching holes in these.


    RG

  8. #8
    Join Date
    Jan 2014
    Location
    NH
    Posts
    136

    Default Re: Vapor Barrier and insulation in walls

    Quote Originally Posted by rae_gordon View Post
    Thanks for all the replies. So unless someone sees a problem with the plastic, I will probably will go that route.


    RG
    Hi, Don't forget to add in the price of removing the plastic after you realize you made a big mistake. Thanks

  9. #9
    Join Date
    Dec 2007
    Location
    Tennessee
    Posts
    1,769

    Default Re: Vapor Barrier and insulation in walls

    Its not going to be a mistake to put up the plastic.

  10. #10
    Join Date
    Jul 2010
    Location
    SoCal
    Posts
    6,699

    Default Re: Vapor Barrier and insulation in walls

    Plastic has been used as a barrier for a very long time with excellent results.

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